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2012 SOUTHEASTERN NATURALIST 11(1):43–48
A New, Non-Destructive Method for Sampling
Jonathan D. Hopper1,* and Alexander D. Huryn1
Abstract - Burrowing crayfish are typically sampled by excavation, which results in
habitat destruction. Several less destructive trapping methods have been devised, though
their results have been inconsistent in our experience. To conduct studies of growth
and longevity, a more efficient method was needed to sample burrowing crayfish while
leaving their burrows intact. We describe a new trap design based on a reversed pitfall
trap. This trap was tested using a population of burrowing crayfish, Cambarus Lacunicambarus
diogenes (Devil Crayfish), in Alabama. The weekly trapping success rate (n =
18 traps) over a 4-week period ranged from 6% to 33%, with an average success rate of
17%. We feel that the implementation of our design will enhance studies requiring nondestructive
Crayfish classified as primary burrowers contribute 15% to total crayfish
species richness, while representing >30% of those listed as critically imperiled
(Eversole and Welch 2010, Hobbs 1981, Hobbs and Lodge 2010, Welch and
Eversole 2006b). Despite their high level of imperilment compared with other
crayfish, relatively little is known about their biology. This lack of knowledge
has been partly caused by the difficulty involved in capturing burrowing species
(Duffy and Thiel 2007), as indicated by the relatively large disparity between
the number of ecological studies devoted to stream- and lake-dwelling species
versus burrowers. At present, the most effective method for capturing burrowing
crayfish is excavation (Ridge et al 2008). There are obvious drawbacks to
this method; besides being labor and time intensive, roots or stones in the soil
matrix surrounding the burrow often prohibit excavation. Moreover, this method
destroys the burrow, a habitat that is sometimes used by juveniles and other organisms
(Duffy and Thiel 2007).
Due to the drawbacks of excavation, a number of burrowing crayfish traps have
been designed (Hobbs 1972, Norrocky 1984, Ridge et al 2008, Welch and Eversole
2006a). The Norrocky burrowing crayfish trap is based on a hinged one-way trap
door in a tube that is inserted into the burrow’s opening (Norrocky 1984). This
trap captures the crayfish within the tube as it makes its way past the trap door. Norrocky
(1984) reported a trap success rate of 13%, but provided no further details of
how this was estimated. The burrowing crayfish net (Welch and Eversole 2006a) is
based on the insertion of avian mist netting into the burrow mouth, which entangles
and captures crayfish as they attempt to exit. This method is ideal when trapping
1University of Alabama, Department of Biological Sciences, Box 870206, Tuscaloosa,
AL 35487. *Corresponding author - firstname.lastname@example.org.
44 Southeastern Naturalist Vol. 11, No. 1
species with large numbers of spines and tubercles, although it shows less promise
when trapping smoother-bodied species (Ridge et al. 2008).
Welch and Eversole (2006a) compared the burrowing crayfish net method
with the Norrocky trap (n = 25 of each trap type, deployed over 7–12 days for 4
sampling periods from February to June 2001), resulting in an average weekly
capture success rate of 4% for the Norrocky trap and 20% for the burrowing crayfi
sh net. Capture success was estimated as the mean of the percent of successful
traps (# crayfish captured/traps deployed) for the four deployments. Ridge et al.
(2008) compared the two methods based on traps deployed at 268 pairs of burrows
and reported capture success rates (# crayfish captured/traps deployed) of
4.5% for the crayfish net and 5.2% for the Norrocky trap. Based on these studies,
the Norrocky trap appears to have a somewhat consistently low success rate. The
capture success rates of the crayfish net are variable, but can be relatively high
(Welch and Eversole 2006a).
In our studies of crayfish in the Sipsey River drainage (Tuscaloosa County,
AL), we attempted to use the crayfish net and the Norrocky trap to capture
crayfish. In our experience based on sampling Cambarus (Lacunicambarus)
diogenes Girard (Devil Crayfish), however, the excavating activities of
crayfish produced significant problems for these trap designs. The net traps
were routinely encased in clay and pushed from the entrances of the burrows
and the tubes of the Norrocky trap became filled with clay rendering the trap
door non-functional. To circumvent problems with these previously devised
methods, we designed a new trap.
Our study was conducted in an open canopy roadside ditch beside the Taylor
Creek headwater stream. This stream is a tributary to the Sipsey River in western
Alabama (33.0964°N 87.8325°W). The site is a well-drained portion of the
Sipsey River flood plain and rarely floods for prolonged periods. The study area
is a roadside drainage ditch approximately 175 m2 in area containing an average
of 0.65 burrows/m2 inhabited by C. Diogenes. The diameters of the burrow openings
ranged 18–49 mm (mean = 29 mm, n = 28).
Trap design and construction
Our design is based on a reversed pitfall trap. This trap is constructed of a covered
bucket with a hole in its bottom. The bucket is placed over a crayfish burrow,
and a modified funnel is inserted into the burrow’s opening. Crayfish emerging
from the burrow fall from the top of the funnel to become trapped within the
bucket (Fig. 1).
Traps were constructed from black plastic 2-gallon (7.75-L) buckets with
20-cm diameter bottoms. The upper part of the bucket was removed, resulting
in a cylinder 10-cm in height. A 7-cm diameter hole was cut into the center
2012 J.D. Hopper and A.D. Huryn 45
of the bottom of the bucket and a funnel was glued into the hole using Liquid
Nails®. Roughly 1-cm of the narrow part of the funnel protruded from the
bottom of the bucket. The funnel was modified so that the top was 14-cm in
diameter and the bottom was 6-cm in diameter. These dimensions were appropriate
given the size of C. diogenes burrows and provide enough room for
the crayfish to move over the top of the funnel when the trap is closed with a
tight-fitting lid. Covering the trap minimized evaporation of water and entry of
predators such as birds and raccoons.
The burrow’s chimney, if present, was removed and the trap was placed
over the burrow opening and pressed firmly into the sediment. Traps were
then partially filled with water to keep captured crayfish from desiccating.
Water was also poured down the burrow itself. In our experience, this enhances
crayfish activity within its burrow and may increase the probability of
capture (J.D. Hopper, pers. observ.).
Figure 1. Upper left: A pair of crayfish traps deployed on burrows of Cambarus diogenes
on the Sipsey River floodplain in Tuscaloosa County, AL. Upper right: Open crayfish
traps showing evidence of crayfish activity (left trap), with the actual capture of the
burrow’s resident (right trap). Lower left: Close up of crayfish trap showing evidence of
crayfish activity without actual capture of the burrow’s resident. Lower right: Close-up
of trap containing captured specimen of C. diogenes.
46 Southeastern Naturalist Vol. 11, No. 1
Recently, it has been suggested that the burrow chimney is of more importance
to the crayfish than simply being a deposition point of sediment
(B. Helms, Department of Biological Sciences, Auburn University, Auburn,
AL, pers. comm.). To deploy the trap, however, the chimney must be removed
to allow the bottom of the trap to be flush with the soil. One of the aims of using
burrow traps is to limit stress on the crayfish in order to conduct long-term
studies. Consequently, chimneys were gently lifted away and placed to the
side of the trap during deployment. Once sampling was completed, chimneys
were replaced. In the event the chimney serves a purpose, its replacement
post-sampling should decrease sampling stress on the population during longterm
In April 2010, we used our new trap design to sample a population of burrowing
Cambarus diogenes within the Sipsey River drainage in Tuscaloosa County,
AL. Eighteen traps were deployed and checked weekly for four weeks. Traps
were graded as “empty” if there was no evidence of crayfish activity, “empty with
evidence of activity” if chimney construction within the funnel was evident, or
“successful” if a crayfish was captured. When traps were found empty after being
deployed for 1 week, they were moved to a new burrow. Traps containing crayfi
sh were also moved to new burrows to avoid recapturing the same individual
over and over. Traps containing sign of crayfish activity were cleaned of excess
sediment and re-deployed on the same burrow.
Table 1. Capture success rate for new trap design. Traps were deployed for four weeks during April
2010. # captured = number of crayfish captured using 18 traps. # activity = number of traps with
evidence of activity (e.g., crayfish captured or construction of a burrow chimney within the trap’s
funnel). # no activity = number of traps showing no evidence of crayfish activity.
Week # captures # evidence # no activity
1 6 8 4
2 3 9 6
3 2 11 5
4 1 11 6
Table 2. Trapping efficiency by trap form. A) Ridge et al. (2008) trapping efficiency over the course
of their study. B) Welch and Eversole (2006a) weekly average trapping efficiency computed from
their data. C) Norrocky (1984) success rate, no data or date range given. D) Weekly average trapping
efficiency for this study.
Weekly average trapping efficiency
Trap form A B C D
Norrocky 5.20% 4.04% 13.00% -
Mist net 4.50% 20.08% - -
New design - - - 16.60%
2012 J.D. Hopper and A.D. Huryn 47
We captured 12 specimens of Cambarus diogenes during the month of
April 2010 (Table 1). Traps were checked 4 days after the initial deployment.
Fifteen of these traps displayed evidence of crayfish activity, yet only one
individual was captured. Seven days after deployment, traps were checked
again (following rain), and an additional 5 crayfish were captured. The rain
also apparently prompted crayfish to increase their digging activities resulting
in the partial filling of some traps with sediment, though there was no
evidence of crayfish being caught and subsequently escaping. The number of
crayfish captured per week ranged from 1 to 6 individuals. Our weekly capture
success thus ranged from 6% to 33%. The average weekly trap success
rate during the entire 4-week study was 17%. Interestingly, the highest number
of captures took place during the first week of sampling, after which the
number of crayfish captured steadily declined, possibly due to the exhaustion
of active burrows. During the first week of deployment, one trap was found
with two crayfish captured from a single burrow. During the second week of
deployment, one dead crayfish was found in a trap. All water in this trap had
evaporated, and the crayfish was apparently dehydrated. This incident was the
only occurrence of mortality.
In our experience, the Norrocky trap and the burrowing crayfish net were not
successful in capturing C. diogenes from their burrows. We attribute this failure
to the large amounts of clay excavated by crayfish during burrow construction
and maintenance. Our new trap design provides room for the accumulation of
excavated sediment while remaining functional. In addition, it leaves the burrow
intact, requires only temporary removal of the chimney, and provides a waterfi
lled and predator-free refuge for captured specimens. Finally, it is inexpensive
and relatively easy to construct. Given the capture success rate of our new trap,
compared with other published designs (Table 2), it provides an effective alternative
method for sampling burrowing crayfish.
Duffy, J.E., and M. Thiel. 2007. Evolutionary Ecology of Social and Sexual Systems:
Crustaceans as a Model Organism. Oxford University Press, Oxford, UK.
Eversole, A.G., and S.M. Welch. 2010. Conservation of imperiled crayfish: Distocambarus
(Fitzcambarus) youngineri Hobbs and Carlson 1985 (Decapoda: Cambaridae).
Journal of Crustacean Biology 30:151–155.
Hobbs, H.H., Jr. 1972. Crayfishes (Astacidae) of North and Middle America. Biota of
Freshwater Ecosystems. Identification Manual No. 9. US Environmental Protection
Agency, Washington, DC. 173 pp.
Hobbs, H.H., Jr. 1981. The Crayfishes of Georgia. Smithsonian Contributions to Zoology
48 Southeastern Naturalist Vol. 11, No. 1
Hobbs, H.H., III, and D.M. Lodge. 2010. Chapter 22. Decapoda. Pp. 901–967, In J.H.
Thorp and A.P. Covich (Eds.). Ecology and Classification of North American Freshwater
Invertebrates, Third Edition. Academic Press, Elsevier, London, UK.
Norrocky, M.J. 1984. Burrowing crayfish trap. Ohio Journal of Science 84:65–66.
Ridge, J., T.P. Simon, D. Karns, and J. Robb. 2008 Comparison of Three Burrowing
Crayfish Capture Methods Based on Relationships with Species Morphology, Seasonality,
and Habitat Quality. Journal of Crustacean Biology 28:466–472.
Welch, S.M., and A.G. Eversole. 2006a. Comparison of two burrowing crayfish trapping
methods. Southeastern Naturalist 5:127–30.
Welch, S.M., and A.G. Eversole. 2006b. The occurrence of primary burrowing crayfish
in terrestrial habitats. Biological Conservation 130(3):458–464.